SEQUENCE STRATIGRAPHIC DISTRIBUTION OF THE CLAY MINERAL CORRENSITE IN TWO CONTRASTING DEPOSITIONAL ENVIRONMENTS OF MISSISSIPPIAN AGE: EVIDENCE FROM NORTHWEST GEORGIA AND NORTH CENTRAL TENNESSEE

X-ray diffraction (XRD) analysis of clay minerals separated from carbonate rock collected within a high resolution sequence stratigraphic framework from two Mississippian aged sequences interpreted by conventional facies analysis to be deposited within restricted marine and normal marine environments respectively provide context to test the potential for corrensite to serve as a sequence boundary proxy in carbonates deposited during semiarid-arid conditions. Corrensite is a regularly ordered (50:50) interstratified chlorite-smectite clay mineral shown to be an intermediate phase in the Mg-smectite to Mg-chlorite transition with increasing temperature and pressure. Studies of modern restricted marine environments suggest precursor minerals to corrensite form authigenically. XRD analysis of clay minerals separated from limestones within a sequence of the Tuscumbia and Monteagle Formations in northwest Georgia reveal the presence of corrensite in association with sequence boundaries and late highstand systems tract (HST) deposits. During the late HST, corrensite appears progressively deeper within each succeeding parasequence cycle suggesting marine water became increasingly restricted during each ensuing phase of parasequence development prior to subaerial exposure. Transgresive systems tract (TST) and early HST deposits contained smectite, illite and minor kaolinite. In contrast, corrensite is present throughout the TST and HST of a restricted marine sequence of the Saint Louis Formation in Jellico, Tennessee. These data illustrate how linking clay mineral diagenesis to a high resolution sequence stratigraphic framework can provide valuable information concerning the position of sequence boundaries and the extent of hypersaline reflux on sediment deposited within semiarid-arid settings.